The development of CNS tissue from inbred normal and neurological mutant mice will be studied by placing immature CNS tissue in organotypic culture. Light and electron microscopic examination of cultures will be used to analyze the role of intrinsic versus extrinsic factors in normal CNS development and in the mechanism of the mutant diseases. Myelinogenesis, synaptogenesis, and large-scale rearrangements of developing neurons into appropriate adult patterns are obtained in cultures of cerebellum and hippocampal formation. Normal in vitro neuroanatomy is well though not completely worked out for cerebellum, but requires much further investigation for hippocampus. If tissue from a mutant develops more anatomy in vitro than in vivo this proves that the defect is extrinsic to the affected tissue. The extrinsic factors can then be pursued, using the culture system as a test object. If the disease is reproduced in vitro and appears intrinsic, further manipulation of the culture system may help to define its mechanism. A disease may be intrinsic to a CNS region but extrinsic to the specific cell type affected. This will be tested by combining dissociated cell fractions from CNS of one genotype in culture with appropriate collaborator cells of another genotype. Marker genes will be essential for identification of genotypes before expression of the disease. One mutant, jimpy, which is deficient in CNS myelin, has already been studied in culture. The disease is intrinsic, but jimpy axons must be tested for their ability to accept myelination by normal oligodendroglia. Other mutants ready for culture study include quaking and msd, both deficient in CNS myelin; staggerer and weaver, which both lose all cerebellar granule cells, but by different mechanisms; and reeler, which has disordered pattern formation in cerebral isocortex, hippocampal formation, and cerebellum. Many other mutants have as yet received little or no neuroanatomical examination, and these will be screened, in collaboration with Prof. R.L. Sidman, Harvard Medical School, for anatomical abnormalities which might be promising for in vitro experimentation.